Disulfiram, a drug used for the treatment of alcohol abuse for more than 50 years has been shown to reduce cocaine use in cocaine-dependent patients. This effect is independent of alcohol use. The mechanism by which disulfiram reduces cocaine use is unknown. Disulfiram is a prodrug and is metabolized by the cytochrome P450 system to a number of chemical intermediates. Inhibition of liver mitochondrial aldehyde dehydrogenase (ALDH2), the pharmacological basis for its use in alcoholism treatment, is due to S-methyl N, N-diethylthiolcarbamate sulfoxide (DETC-MeSO). Studies suggest that DETC-MeSO is metabolized to S-(N, Ndiethylcarbamoyl) glutathione (carbamathione). In vivo, carbamathione has no effect on ALDH2, but inhibits glutamate binding in synaptic membranes of brain homogenate. Thus, disulfiram may have two pharmacological effects, a peripheral action as an ALDH2 inhibitor and a central effect on the glutamatergic system. In this exploratory and developmental research grant application a series of studies will be carried out to obtain the preliminary data needed as the basis for more extensive studies investigating carbamathione's mechanism of action. Analytical and pharmacodynamic studies will be the focus of this application. Determination of carbamathione by mass spectrometry has already been developed. The present studies will develop the mass spectrometric and fluorometric methods for determining DETC-MeSO, carbamathione, and dopamine, glutamate, and GABA. In the pharmacodynamic studies, rats will be surgically prepared and a probe implanted into the nucleus accumbens and in the vena cava for determining brain dialysate and blood concentrations of DETC-MeSO and carbamathione simultaneously using a two-probe technique. Rats will be treated with disulfiram, DETC-MeSO, and carbamathione, and using microdialysis techniques, determine if DETC-MeSO and carbamathione can be found in brain dialysate and blood. The simultaneous determination of brain carbamathione, and dopamine, glutamate and GABA also will be carried out. Simultaneous analysis of blood and brain for DETC-MeSO and carbamathione would provide information as to whether carbamathione is formed peripherally or in the brain. Finding carbamathione in brain dialysate after disulfiram and DETCMeSO administration would provide support for future studies on the effect of carbamathione in a cocaine animal model. The significance of this research is that carbamathione can be used as a pharmacological tool to better delineate the mechanism of action of disulfiram in cocaine dependence and perhaps design better and more selective agents. Clinically, carbamathione may be a better drug candidate than disulfiram for treating cocaine dependence since carbamathione is not dependent upon the cytochrome P450 enzymes, and hence can provide a more potent, specific, and consistent therapeutic effect than disulfiram.
